1. Field
Example embodiments generally relate to fuel structures used in nuclear power plants and methods for using fuel structures.
2. Description of Related Art
Generally, nuclear power plants include a reactor core having fissile fuel arranged therein to produce power by nuclear fission. A common design in U.S. nuclear power plants is to arrange fuel in a plurality of cladded fuel rods bound together as a fuel assembly, or fuel assembly, placed within the reactor core. These fuel assemblies may include one or more interior channels, or water rods, that permit fluid coolant and/or moderator to pass through the assembly and provide interior heat transfer/neutron moderation without significant boiling.
As shown in FIG. 1, a conventional fuel assembly 10 of a nuclear reactor, such as a BWR, may include an outer channel 12 surrounding an upper tie plate 14 and a lower tie plate 16. A plurality of full length fuel rods 18 and/or part length fuel rods 19 may be arranged in a matrix within the fuel assembly 10 and pass through a plurality of spacers (also known as spacer grids) 20 axially spaced one from the other and maintaining the rods 18, 19 in the given matrix thereof. The fuel rods 18 and 19 are generally continuous from their base to terminal, which, in the case of the full length fuel rod 18, is from the lower tie plate 16 to the upper tie plate 14.
One or more water rods 22 may be present in an interior or central position of assembly 10. Water rods 22 may extend the full-length of assembly 10 or terminate at a desired level to provide fluid coolant/moderator throughout assembly 10. Water rods 22 may be continuous, preventing fluid from flowing outside the rods 22, or perforated, segmented, or otherwise broken to permit fluid coolant moderator to flow between rods 22 and the remainder of assembly 10.
FIGS. 2A-2D are axial cross-section illustrations of conventional 10×10 fuel assemblies like those shown in FIG. 1, showing various water rod configurations in conventional assemblies. As shown in FIGS. 2A-2D, water rods 22 may be a variety of lengths (such as full-length or part-length), sizes (for example, rod-sized cross-section or larger), and shapes (including circular, rectangular, peanut-shaped, etc.). Similarly, any number of distinct rods 22 may be present in conventional assemblies 10, depending on the desired neutronic characteristics of assemblies having the water rods 22. Water rods 22 may be symmetric about an assembly center, as shown in FIGS. 2A and 2D, or offset as shown in FIGS. 2B and 2C.